Some papers classified as decorative papers are used to make decorative laminates. The top sheets of paper in decorative laminates may or may not be printed with a decorative pattern either before or after being saturated (or impregnated) with resin and then they are laminated under elevated pressures and temperatures onto a variety of substrates from paper to composites and wood. Decorative laminates are often used to simulate wood grains and other designs and used in the manufacture of floors, furniture etc. An exemplary product is referred to as Formica.
In such products, the saturated decorative paper (the top sheet) must have enough opacity (hiding power) to cover and hide the dark substrate underneath so that the dark substrate does not interfere with the aesthetics of the printed pattern. However, since the decorative paper is saturated with materials that are similar in refractive index to the paper fiber, the saturated paper is transparent unless it contains fillers such as titanium dioxide that have a higher refractive index. High refractive index fillers are expensive; therefore, less expensive fillers are used to extend the titanium dioxide. These might include kaolin fillers, special talcs and calcined kaolin. The black glass scattering coefficient of a commercially available calcined kaolin is 0.284 m2/g at 457 nm. And since a substantial amount of decorative papers to be laminated are used in laminates that are white or off-white in color, a high degree of brightness and whiteness are also desired.
The Engelhard product brochure on EXCALIBER® high opacity kaolin-based pigment (published 2002) teaches that this product having a GE brightness of 83% or less can be used in paper applications that do not require high brightness. For example it has been used in Lightweight Coated Paper (LWC) and decorative laminates.
International Publication Number WO 00/32700 teaches a heated mixture of 90% metakaolin and 10% anatase titanium dioxide (Kronos 1000 from Kronos Inc.) which can be used as a filler and coating pigment. The reported GE brightness for this heated mixture is 85.2.
International Publication Number WO 00/32700 teaches a pigment of a heated mixture of 90% hydrous kaolin and 10% rutile titanium dioxide (RCS VANTAGE from DuPont) which can be used as a filler and coating pigment. As shown in Preparation A below, a heated mixture of 89.5% hydrous kaolin and 10.5% rutile titanium dioxide has a GE brightness of 81.3% and a Hunter yellowness index of 11.60. Although we understand that a mixture similar to the Preparation A mixture has been used in a décor paper that was sold, such a mixture is undesirable in white grades of décor paper because it results in low brightness, poor whiteness and yellow appearance.